The present invention relates to a communication system and more particularly to a communication system via high noise transmission lines of low-voltage power such as an electric wire and its sender and receiver.
Such narrow-band noises as distortion and impulse noise in transmission lines are often too great to overlook in the transmission systems. In such transmission systems a diffusion data transmission technique has been used as useful means to combat those noises in the past. The diffusion data transmission technique comprises the sender which diffuses data to send via a transmission line and the receiver which inversely diffuses data received The data transmission system based on that conventional diffusion data transmission is described by the following example of the data transmission system using the existing electric power line, that is, low-tension power line of a 100-volt a. c., 50/60 Hz.
FIG. 15 is a block diagram showing an example of the conventional system of the direct diffusion technique for sending data via the electric power line.
In FIG. 15, a sender 100 and a receiver 200 are connected to each other via a transmission line 300.
The sender 100 is provided with a mixer 110, a pseudo noise generator 111, a carrier wave oscillator 112 and an equilibrium modulator 113. The receiver 200 includes a mixer 210, a pseudo noise generator 211, a carrier wave oscillator 212, an equilibrium modulator 213 and an intermediate frequency band pass filter (IF-BPF) 214.
Diffusion signals from the pseudo noise oscillator 211 is inputted in the mixer 110 on the sender side as well as input data are inputted in the same
Those two kinds of signals are multiplied and inputted in the next equilibrium modulator 113 The aforesaid carrier wave oscillator 112 generates and inputs a carrier wave in the equilibrium modulator 113. The equilibrium modulator 113 then modulates the carrier wave with the signal from the mixer 110 (diffused input signal) and sends out the modulated carrier wave without the original carrier wave to the receiver 200.
In the receiver 200, the carrier wave oscillator 212 generates a carrier wave with the same frequency as of the carrier wave generated by the carrier wave oscillator 112 on the side of the sender 100, and inputs it in the equilibrium modulator 213. Meantime, the pseudo noise generator 211 produces an inversely diffused code with a phase opposite to the diffused code generated by the sender 100, and inputs it in the equilibrium modulator 213. Thereby, the equilibrium modulator 213 modulates the carrier wave outputted from the carrier wave oscillator 212 by using an inversely diffused code outputted by the pseudo noise generator 211. The modulated carrier wave is then outputted to the mixer 210. The mixer 210 multiplies a modulated signal inputted via the transmission line 300 and a modulated signal inputted from the equilibrium modulator 213, and then outputs its result to IF-BPF 214. IF-BPF 214, which means an intermediate frequency band pass filter, is a filter through which waves in the intermediate frequency band can pass.
Now, supposing that the data signal inputted to the mixer 110 carries a spectrum as shown in FIG. 16(a), the mixer 110 diffuses the spectrum by multiplying the input data signal using the diffused code provided by the pseudo noise generator 111. A spectrum waveform of an input data signal after the diffusion is shown in FIG. 16(b). The diffused data signal then modulates a carrier wave outputted from the carrier wave oscillator 112 at the equilibrium modulator 112 and outputs the modulated signal onto the transmission line 300. The phrase diffused code means a code with multiple bits in relation to xe2x80x9c1xe2x80x9d or xe2x80x9c0xe2x80x9d as, for example, a 31-bit code like 1111100011011101010000100101100 or 0000011100100010101111011010011.
The following is described in the case that an impulse noise (shaded area indicated in FIG. 16(c)) occurs while data signals are being sent via the transmission line 300 and the receiver 200 is to receive the signals shown in FIG. 16(c).
As mentioned, the carrier wave outputted by the carrier wave oscillator 212 in the receiver 200 is modulated with the inversely diffused code given by the pseudo noise generator 211 at the equilibrium modulator 213 Furthermore, the mixer 210 diffuses the spectrum by multiplying the modulated signal and the diffused data signal obtained via the transmission line 300. The inversely diffused code is a code that the total bits of the diffused code is xe2x80x9c1xe2x80x9d against the inputting of xe2x80x9c1xe2x80x9d if the absolute OR with the diffused code is taken (reversely, the inputting xe2x80x9c0xe2x80x9d brings the total bits of the diffused code to xe2x80x9c0xe2x80x9d), that is, the inversely diffused code is a code that the diffused code is turned round.
In the multiplication performed at the mixer 210, the data signals diffused at the sender 100 will be inversely diffused but will undergo usual diffusion against the impulse noise. Therefore, the spectrum waveform of data signals after the multiplication (that is, an inverse diffusion) is as shown in FIG. 16(d). That is, the data signals are recovered to the original form while the impulse signals generated in transmission are diffused instead so that the level for the data signals gets small immediately. This way, the effect of the impulse signals upon the data signals is alleviated
Needless to say, however, in order to carry out the aforesaid inverse diffusion exactly, it is necessary to exactly synchronize the inputting in the mixer 210 of signals from the transmission line and the inputting of modulated signals from the equilibrium modulator 213.
As set forth above, the conventional system of sending data by direct diffusion technique alleviates the effects of narrow band noises such as impulse noise as well as distortion on the transmission line caused by equipment connected to the line, (for example, the line noise occurring at the start-up of the compressor in the household refrigerator connected to the low-tension electric power line through the 100 V outlet in the house), by the processing of diffusing and inversely diffusing the spectrum as indicated in FIGS. 16(c) and 16(d).
The technique of diffusing spectrum is described in a book entitled xe2x80x9cSpectrum Diffusion Communication Formulaxe2x80x9d published by Jatech Publishing Co., pages 9 to 28.
The prior art system of sending data by the direct diffusion technique as just outlined is effective in removing the effects of narrow-band noises and line distortion to some extent. But in the prior art, it is impossible to completely get rid of the effects of narrow-band noises and line distortion over the full band of frequencies as in the low-tension power line. That is, in case the line noise or distortion is too strong over the level of input data signals, the conventional diffusion technique is no longer effective enough to reduce those noises or distortion.
And, since the frequencies of the aforesaid diffused code are spread over a wide band the bandwidth occupied by the modulated signals increases. Accordingly a large number of side lobes rises over a wide band as well as a main lobe, and those side lobes consume much energy and keeps down the transmission efficiency As mentioned furthermore, the inverse diffusion requires the synchronizing of signals obtained from the transmission line and signals from the equilibrium modulator. This synchronizing undergoes complicated procedures and costs much when it is carried out through a fairly complicated circuit or program In addition the prior art is not sufficient in synchronizing accuracy and can fail to detect data.
It is an object of the present invention to provide a communication system for transmitting data at a high speed with the data quality kept high by making good use of frequency bands which are free from the effects of narrow band noises or line distortion. It is another object of the present invention to provide a communication system which can improve transmission efficiency and accuracy through the use of a plurality of carriers with the frequencies assuming values at specific intervals.
To achieve the foregoing objects, the present invention adopts a number of means described below. And it is prerequisite that the present invention adopts a communication system in which a sender 1 and a receiver 2 are connected to each other via the transmission line. That communication system is the basis on which the present invention is built.
First, according to the above prerequisite arrangement, the basis communication system is provided with a sending signal generating means 10 as at, shown in FIG. 1 and FIG. 6. The sending signal generating means 10 output converted data after converting an input signal into a plurality of carrier signals assuming values at such intervals on the axis of frequency that the frequencies may not interfere with each other. If an interfering noise with any one of the plurality of frequencies arises on the transmission line, removal of only a carrier of the noise frequency would leave the communication in a good condition.
The sending signal generating means 10 is formed of a carrier signal generating means 12 for generating signals with frequencies assuming values at specific intervals, and a multiplication means 11 for sending out the input signals on the transmission line after multiplying them by the respective carrier signals and then.
A transmission line characteristics measuring means 20 is provided on the receiver 2 to find the characteristics on the transmission line, and on the basis of the results from the transmission line characteristics measuring means 20, a selection control means 40 provided to the sender 1 or the receiver 2 judges whether a noise arises on the transmission line or not.
The selection control means 40 incorporates the results in the sending signals from the sender 1 or in the receiving signals to be inputted in the receiver 2 via the transmission line.
In other words, the selection control means 40 controls the generation of carrier signals at a carrier signal generating means 12 in the sender 1, as shown in FIG. 6 and FIG. 8 so that the selection control means 40 does not send out carrier signals with poor characteristics on the transmission line. Or decreases the ratio of carrier signals with poor characteristics on the transmission lines. Or the selection control means 40 does not pick out and commit to synthesis the carrier signals with poor transmission line characteristics in forming the signals to be received by the receiver 2 as illustrated in FIG. 1. Or the means 40 reduces the percentage in the synthesis of the carrier signals with poor transmission lines characteristics.
The transmission line characteristics measuring means 20 determines line characteristics on the basis of the absolute value of the intensity of receiving signals as shown in FIG. 3 and FIG. 7 or on the basis of the phase difference from the reference phase and inputs the results in the selection control means 40.
Still better results can be hoped for if the respective carrier signals are so arranged as not to interfere with each other or so arranged to intersect orthogonally with each other not only on the axis of frequency but also on the axis of time as shown in FIG. 13 and FIG. 14.
That is to say, it is so arranged that the sender 1 generates carrier signals by passing the input signals through a plurality of filters 52 which satisfy the orthogonal requirements both on the axis of frequency and the axis of time (double orthogonalization). On the other hand the receiver 2 uses a plurality of filters 62 which form only the same but time-delayed with sending signals. That can form signals with a band narrow not only on the axis of frequency but also on the axis of timexe2x80x94the sending signals largely not subject to the effects of noises arising on the transmission line.
In that case, it is also desirable to eliminate or reduce the mixing ratio of the carriers which flow through the transmission lines with poor characteristics.
For a plurality of types of input signals, it is, in principle, necessary to provide a plurality of sets of the sending signal generating means 10. In case the aforementioned double orthogonalization is used, it is desirable that the encoder should have a function of allocating the filters, for example, filters a to c for input A and filter d to f for input B, since an encoder is used to divide the input signals in the number corresponding to a plurality of filter.